chapter 11 Flashcards
(50 cards)
What is the primary function of gene regulation in bacteria?
To control the levels of gene transcription and RNA translation
Gene regulation allows bacteria to adapt to environmental changes and manage energy expenditure efficiently.
What are the two main types of regulation in bacterial gene expression?
Positive and negative regulation
Positive regulation requires an activator protein for transcription, while negative regulation requires the absence of a repressor.
What is the role of the lac repressor protein?
To bind to the lac operator DNA and prevent transcription of the lac operon
The lac repressor is encoded by the I gene and acts negatively on gene expression.
What happens when lactose is present in relation to the lac operon?
Lactose binds to the Lac repressor, causing an allosteric transition that allows transcription to occur
This process is known as induction.
Define ‘operon’.
A DNA segment encoding a multigenic mRNA for genes sharing an adjacent promoter and regulatory region
The lac operon includes segments P, O, Z, Y, and A.
What is catabolite repression?
A regulatory mechanism where the presence of glucose inhibits the production of enzymes for metabolizing other sugars like lactose
This is an example of prioritizing energy sources.
What is the role of cAMP in the regulation of the lac operon?
cAMP acts as an allosteric effector of the catabolite activator protein (CAP), enhancing transcription when glucose levels are low
High glucose levels lead to low cAMP levels, inhibiting lac operon expression.
What constitutes a genetic switch?
The functional relationship between regulatory proteins and binding sites within a DNA sequence that controls gene transcription
These switches determine whether genes are expressed.
What are operators in the context of bacterial gene regulation?
DNA sequences near the promoter that serve as binding sites for repressor proteins
Operators play a critical role in negative regulation.
What do the Z, Y, and A genes in the lac operon encode?
- Z gene encodes β-galactosidase
- Y gene encodes permease
- A gene encodes a transacetylase
These genes are coordinately regulated to metabolize lactose.
True or False: The lac operon is an example of both positive and negative control.
True
The operon utilizes both a repressor (negative control) and CAP (positive control).
What is the function of allosteric effectors?
To bind to regulatory proteins and modify their shape and function
This interaction can activate or inactivate the regulatory protein.
Fill in the blank: The _______ is the site on DNA where RNA polymerase binds to initiate transcription.
[lac promoter]
The lac promoter is crucial for the transcription of the lac operon genes.
What is the significance of Jacob and Monod’s studies on lactose metabolism?
They provided insights into gene regulation mechanisms and the genetic basis of the lac operon
Their work laid foundational knowledge for understanding operons in prokaryotes.
What are constitutive mutations?
Mutations where lac operon genes are expressed regardless of the presence of an inducer
These mutations reveal insights into the regulatory mechanisms of the lac operon.
What does it mean for a mutation to be cis-acting?
It regulates the expression of an adjacent transcription unit on the same DNA molecule
Operator mutations are an example of cis-acting mutations.
What is the role of CAP in the lac operon?
CAP activates transcription of the lac operon when cAMP is present
This is part of the positive control mechanism for the operon.
What is the function of the Lac repressor in the absence of lactose?
It binds to the operator and prevents transcription of the lac operon
This is a key aspect of negative regulation.
How does glucose influence the lac operon?
High glucose levels inhibit cAMP production, preventing activation of the lac operon
This demonstrates catabolite repression in bacterial metabolism.
What type of regulatory proteins control the lac operon?
Positive – CAP, Negative – Lac repressor
What does the arabinose (ara) operon include?
Genes for enzymes that break down arabinose
What are the upstream regulatory sequences of the ara operon?
Promoter (P), initiator (I), and operator (O)
What does the araC gene encode?
A transcription factor protein called AraC
What initiates transcription in positive regulation of the ara operon?
Binding of AraC protein to the araI region when bound by arabinose
